Oil rig platforms and the like are well known in the art. These platforms are commonly used during construction of the oil rig and to support workers and equipment at desired elevations. Platforms are necessarily moved upward and downward and these platforms are known as elevating platform assemblies. It is necessary to lift and lower large loads on oil rig platforms and the like. It is necessary to quickly change the elevation of workers and equipment and thus, elevating platform assemblies are advantageous. Accordingly, jacking drives are securely attached to the platform along with a motor to power the jacking drives thus raising and lowering the platform to the desired elevation.
United States Patent Publication No. US 2007/0295136 A1 states, in the abstract: “[a]n anti-backlash system comprising a single drive pinion and motor is disclosed. In an exemplary embodiment, the single drive pinion is situated between two idler gears and is allowed to move in the radial direction relative to the bull gear. A preload force provides for the substantial absence of backlash at low torque loads. The pinion moves to the center point between the two idler gears and balances the torque during high torque loads. The present anti-backlash system is well suited for use in drive and positioning systems that are subject to variable and reversing loads, such as those experienced by radio telescopes in variable wind conditions.”
European Patent EP 1 128 974 B1 states, in claim 1, thereof: “[t]he invention relates to a portal drive for a portal axle featuring a drive pinion (1), which is axially supported via two bilaterally arranged axial bearings (4, 5), with the drive pinion driving an output pinion (3) via intermediate gears (2), with which it meshes, characterized in that each of the two axial bearings (4, 5) is pre loaded in axial direction by a spring element (7) so that the drive pinion (1) is floating mounted within the kinetic range of the spring elements (7).”
U.S. Pat. No. 5,595,251, states, in the abstract: “[m]ethods and apparatus are provided for a torque driver including a displaceable gear to limit torque transfer to a fastener at a precisely controlled torque limit. A biasing assembly biases a first gear into engagement with a second gear for torque transfer between the first and second gear. The biasing assembly includes a pressurized cylinder controlled at a constant pressure that corresponds to a torque limit. A calibrated gage and valve is used to set the desired torque limit. One or more coiled output linkages connect the first gear with the fastener adaptor which may be a socket for a nut. A gear tooth profile provides a separation force that overcomes the bias to limit torque at the desired torque limit. Multiple fasteners may be rotated simultaneously to a desired torque limit if additional output spur gears are provided. The torque limit is adjustable and may be different for fasteners within the same fastener configuration.”
Imperfections may occur in the teeth of the rack and the teeth of the pinion which drives the rack. Imperfections may occur in the assembly of the torque sharing drive. Imperfections may occur in the alignment and mounting of the torque sharing drive. Imperfections include dimensional variations and inaccuracies. The dimensional variations may affect: tooth surfaces including flank surfaces, circular tooth thicknesses, circular pitch lengths, and tooth spaces. Inaccuracies include gear tooth spacing or index variation between teeth. Additionally, there may also be inaccuracies in the torque sharing drive assembly mounting and spacing between components thereof.
Individual quality level attributes include the following: for the pinion, lead variation, involute variation, gear tooth spacing/pitch variation. In addition, there are various composite variations, which represent a combination of these individual variations, and more closely represent what actual pinion teeth would present to its mating rack. The rack will have similar variations inherent to its manufacture and quality level. In addition to these dimensional variations inherent in each individual part (pinion and rack), there are mounting and alignment variations inherent in the structure that the rack and pinion (torque sharing drive) mount to. The combined effect of these variations (individual, composite and mounting) can be significant. These variations impact operation of the rack and pinion and affect smooth, completely consistent and conjugate action of the rack and pinion. This is normal and expected for any rack and pinion design. Additionally, backlash is the amount of clearance between the rack and pinion tooth flanks. The amount of clearance necessary depends on alignment accuracy between the rack and the pinion. Dimensional variations/inaccuracies in the teeth of the rack may occur. Pitch deviation is the difference between the theoretical rack length and its actual length and depends on the quality of the rack. Tooth quality depends on the accuracy of tooth flanks and faces. This list is set forth by way of example only and is not exhaustive or complete.